ZOOLOGY 379 



tozoon, in the same way as any other resting cell is activated 

 when in intimate contact with an active neighbour. After 

 activation normal development only occurs if two asters are 

 present in the egg." 



Other recent papers are : 



Herter, K., " Ein Fall von echter Entwicklungskorrelation aus der Natur 



bei Rana esculenta L.," Archiv fiir Entwick. der Organ., July 1922. 

 Maurer, F., " Saugetierhaare und Tastflecke," Anat. Anz., Bd. 56, No. 3. 

 PiNNEY, E., " The Initial Block to Normal Development in Cross-fertilised 



Eggs : (i) Crosses with the Egg of Fundulus ; (ii) Reciprocal Crosses 



between Ctenolabrus and Prionotus," Jr. of Morph., vol. xxxvi, No. 3. 

 Plate, L., " Uber die phylogenetische Entstehung der Milchdriisen und 



Haare," Anat. Anz., Bd. 56, No. 3. 

 Takagi, K., " A Cytological Study on the Dog's Thyroid Gland," Folia 



Anatomica Japonica, Sept. 1922. 

 Verne, J., " Contribution a I'etude des reins aglomerulaires ; I'appariel 



renal des Poissons Lophobranches," Archiv. d'Anat. Micr., Tome xviii, 



Fasc. 4. 



General and Experimental Embryology.— B. G. Smith has 

 carried out a series of experiments with the eggs of Crypto- 

 branchus allegheniensis, with the view to determining the origin 

 of bilateral symmetry in the embryo (" The Origin of Bilateral 

 Symmetry in the Embryo of Cryptobranchus allegheniensis," 

 Jr. of Morph., vol. xxxvi, No. 3, June 1922). It was found that 

 the action of gravity in the direction perpendicular to the polar 

 axis of the egg during the fertilisation period, was without 

 perceptible effect in determining the direction of the median 

 plane of the embryo. The direction of the entrance of the 

 sperm is not an important factor. Although the first cleavage 

 furrow forms approximately at right angles to the direction of 

 the path of entry of the sperm, yet the direction of the first 

 cleavage bears no fixed relation to the direction of the future 

 median plane of the embryo. In the early blastula stages, the 

 direction of eccentric development of the micromeres bears no 

 constant relation to the direction of the median plane of the 

 embryo. In late stages of the blastula, the bilateral symmetry 

 is manifested by the superficial segmentation pattern and by 

 the internal structure, and this condition is undoubtedly the 

 primary expression of the definitive bilateral symmetry of the 

 embryo. 



G. R. de Beer describes " The Segmentation of the Head in 

 Squalus acanthias " in the Q.J. M.S., vol. Ixvi, Part III, 

 Sept. 1922). He finds that Balfour's interpretation of the 

 somites of the head is correct, and free from the objections 

 which accompany Van Wijhe's. " No gill-slit or arch has been 

 lost in the neighbourhood of the hyoid arch. Nine segments 

 are included in the head of Squalus, of which three are pre-otic 



